SPRING PEA AND CANOLA SEEDING RATE TRIALS

Simon Fordyce¹, Sally Dahlhausen¹, McKenna Volkman¹, and Patrick Carr¹

¹Montana State University Dep. Research Centers, Central Agricultural Research Center, Moccasin, MT

Summary

Seed costs can represent a major input in spring pea and canola production. Seeding rate decisions are not always based on local knowledge but can have significant consequences for an operation’s bottom line. Soils of the Judith Basin are notoriously shallow with limited water storage capacity. It is theorized that crops established in shallow soils are opportunists and must rely more heavily on lateral branching to optimize water and nutrient use efficiencies. However, higher seeding rates are known to reduce lateral branching of roots in most crops which could affect the root system’s ability to obtain sufficient water and nutrients for optimal seed yield. This study sought to determine whether ‘optimal’ seeding rates for spring pea and canola in a shallow soil environment are lower than what is currently recommended for the state of Montana. The experiments consisted of five seeding rates for each crop: 5, 7, 9, 11, and 13 pure live seeds per square feet (pls/ft²) for pea and 5, 8, 11, 14, and 17 pls/ft² for canola. Treatments were planted in 75-ft² plots in an experimental design to determine seeding rate differences. Replicates of the 2021 canola trial appeared to capture a local gradient in soil profile depth, offering an opportunity to assess whether the ability of canola seeding rate to impact yield depended on soil profile depth. Spatial patterns in replicates and canola growth were consistent with known vegetative patterns related to soil depth variation. Canola seed yield increased with increasing seeding rate in the shallower replicates but decreased with increasing seeding rate in the deeper replicates, suggesting that the ability of seeding rate to impact canola seed yield depended on the depth of the soil profile (data not provided). However, analyzing all the replicates together, as generally is done, resulted in a failure to detect seed yield differences (Table 1). Replicates of the 2022 canola trial did not span a gradient in soil depth, and yields were much higher overall (1543 lb/ac in 2022 versus 76 lb/ac in 2021), likely due to an earlier planting date (early April in 2022 versus late April in 2021) and precipitation timing differences. Despite higher yields and lower variation in 2022 canola yield data, seeding rate had no statistical effect on seed yield (Table 2). Similarly, seeding rate had no impact on spring pea seed yield in 2021 (Table 3) or 2022 (Table 4). Although more work is needed to understand net revenue responses to changes in pea and canola seeding rates, results of the current experiment suggest that seeding rate reductions of up to 50% confer no significant yield penalties to spring field pea nor to spring canola in shallow soil environments under severe drought conditions.

Acknowledgements

We are grateful to the Montana Agricultural Experiment Station for providing funding for this research.

Table 1. 2021 Spring canola seeding rate trial, Central Agricultural Research Center, Moccasin, MT.

Table 2. 2022 Spring canola seeding rate trial, Central Agricultural Research Center, Moccasin, MT.

Table 3. 2021 Spring pea seeding rate trial, Central Agricultural Research Center, Moccasin, MT.

Table 4. 2022 Spring pea seeding rate trial, Central Agricultural Research Center, Moccasin, MT.